Method for dehydrochlorination of HCFC-244bb to manufacture HFO-1234yf

Abstract

To provide a process for making 2,3,3,3-tetrafluoropropene (HFO-1234yf).SOLUTION: A method includes providing a composition including 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to a reactor including a heater surface at a surface temperature greater than about 850°F (454°C), and then bringing the composition into contact with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb to make HFO-1234yf.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for producing 2,3,3,3-tetrafluoropropene (HFO-1234yf). Specifically, the present disclosure relates to a method for dehydrochlorination of 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) in the production of HFO-1234yf.

Background Art

[0002] Hydrofluoroolefins (HFOs) such as tetrafluoropropene are known as effective refrigerants, fire extinguishing agents, heat transfer media, aerosol propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, liquid carriers, buffing abrasives, displacement desiccants, and power cycle working fluids. Due to environmental problems suspected to be associated with the use of some of these fluids, including their relatively high global warming potential, it is desirable to use fluids that also have a zero ozone depletion potential (ODP) and the lowest possible global warming potential (GWP). Thus, there is considerable interest in developing environmentally friendly materials for the aforementioned applications.

[0003] HFOs with zero ozone depletion and low global warming potential have been identified as potentially meeting this need. However, the toxicity, boiling point, and other physical properties of such chemicals vary widely between isomers. One HFO with useful properties is 2,3,3,3-tetrafluoropropene (HFO-1234yf or 1234yf).

[0004] HFO-1,2,3,4-yf has been shown to be a low global warming compound with low toxicity and can thus increasingly meet the strict requirements for refrigerants in mobile air conditioning. Thus, compositions containing 1234yf are among the materials that have been developed for use in many applications.

Summary of the Invention

[0005] The present disclosure provides a process for producing 2,3,3,3 - tetrafluoropropene (HFO - 1234yf), which comprises supplying a composition containing 2 - chloro - 1,1,1,2 - tetrafluoropropane (HCFC - 244bb) to a reactor comprising a heater surface with a surface temperature exceeding about 850°F (454°C), and then contacting the composition with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC - 244bb to produce HFO - 1234yf.

[0006] In one aspect of the present disclosure, the present disclosure provides a process for producing 2,3,3,3 - tetrafluoropropene (HFO - 1234yf), the process comprising supplying a composition containing 2 - chloro - 1,1,1,2 - tetrafluoropropane (HCFC - 244bb) to a reactor comprising a heater surface with a surface temperature exceeding about 850°F (454°C), and contacting the composition with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC - 244bb to produce HFO - 1234yf.

[0007] The heater surface can have a surface temperature of from about 870°F (466°C) to about 1,200°F (649°C). The contact time can be from 0.1 second to 9 seconds. In some embodiments, the heater surface can include a catalytic surface. The catalytic surface can include electroless nickel, nickel, stainless steel, nickel - copper alloy, nickel - chromium - iron alloy, nickel - chromium alloy, nickel - chromium - molybdenum, or combinations thereof. In other embodiments, the heater surface may not be a catalytic surface.

[0008] The process may further include vaporizing the composition and then heating the vaporized composition to a temperature of about 575°F (302°C) to 1,200°F (649°C) before feeding the composition to the reactor. The process may further include feeding HFO-1234yf, HCl, and unreacted HCFC-244bb from the reactor to a distillation column, separating HFO-1234yf and HCl from at least a portion of the HCFC-244bb in the distillation column, recycling the separated HCFC-244bb to the composition before vaporizing the composition, feeding the HFO-1234yf and HCl to an HCl separation unit, and separating HCl from the HFO-1234yf to form a product stream containing HFO-1234yf. The product stream may contain HFO-1234yf at a concentration greater than 99.1 wt% without containing HCFC-244bb. The product stream may further contain 1,1,1,2-tetrafluoroethane at a concentration of less than 0.1 wt% without containing HCFC-244bb, as exhibiting a low rate of carbon deposition in the reactor. Heating the vaporized composition may include exchanging heat between the vaporized composition and the HFO-1234yf and HCFC-244bb from the reactor before feeding the HFO-1234yf and HCFC-244bb to the distillation column.

[0009] In another aspect of the present disclosure, the present disclosure provides a process for a process for making 2,3,3,3-tetrafluoropropene (HFO-1234yf), the process comprising vaporizing a composition comprising 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb), dividing the composition into a first portion and a second portion, heating the first portion of the vaporized composition to a temperature of about 575°F (302°C) to 1,200°F (649°C), feeding the composition to a reactor comprising a heater surface with a surface temperature above about 850°F (454°C), contacting the composition with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb to make HFO-1234yf. The reactor can comprise a first stage and a second stage downstream of the first stage. The first portion can be fed to the first stage and the second portion can be fed to the second stage.

[0010] The process can further comprise feeding HFO-1234yf, HCl, and unreacted HCFC-244bb from the reactor to a distillation column, separating HFO-1234yf and HCl from at least a portion of the HCFC-244bb within the distillation column, recycling the separated HCFC-244bb to the composition prior to vaporizing the composition, feeding HFO-1234yf and HCl to an HCl separation unit, separating HCl from the HFO-1234yf to form a product stream comprising HFO-1234yf. The product stream can comprise HFO-1234yf at a concentration greater than 99.1 wt% without containing HCFC-244bb. The product stream can further comprise 1,1,1,2-tetrafluoroethane at a concentration of less than 0.1 wt% without containing HCFC-244bb, as showing a low rate of carbon deposition within the reactor.

[0011] Heating the first portion of the vaporized composition may involve exchanging heat between the first portion of the vaporized composition and HFO-1234yf and HCFC-244bb from the reactor before feeding HFO-1234yf and HCFC-244bb to the distillation column. The heater surface can have a surface temperature of from about 870°F (466°C) to about 1,200°F (649°C). The contact time can be from 0.1 second to 9 seconds. The heater surface can include a catalyst surface. The heater surface may not be a catalyst surface.

[0012] Referring to the following description of the embodiments in view of the accompanying drawings, the above and other characteristics of the disclosure, as well as the manner in which they are achieved, will become more apparent and better understood.

Brief Description of the Drawings

[0013]

Figure 1

[0014]

Figure 2

Modes for Carrying Out the Invention

[0015] U.S. Patent No. 8,058,486, titled "INTEGRATED PROCESS TO PRODUCE 2,3,3,3-TETRAFLUOROPROPENE" (issued on November 15, 2011), U.S. Patent No. 8,975,454, titled "PROCESS FOR PRODUCING 2,3,3,3-TETRAFLUOROPROPENE" (issued on March 10, 2015), and U.S. Patent No. 8,766,020, titled "PROCESS FOR PRODUCING 2,3,3,3-TETRAFLUOROPROPENE" (issued on July 1, 2014), various methods for producing HFO-1234yf are known, and the entire content is hereby incorporated by reference into this specification.

[0016] The production of HFO-1234yf from 1,1,2,3-tetrachloropropene (HCO-1230xa, or 1230xa) and hydrogen fluoride can be generalized in a three-step process. Step 1 can be understood as generating 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf, or 1233xf) from 1230xa in a vapor-phase reactor according to the following reaction scheme.

Chemical formula

[0017] Step 2 can be understood as generating 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb or 244bb) from 1233xf in a reactor such as a liquid-phase reactor according to the following reaction scheme.

Chemical formula

[0018] Process 3 can be understood as a dehydrochlorination reaction that produces 2,3,3,3 - tetrafluoropropene (HFO - 1234yf) from 2 - chloro - 1,1,1,2 - tetrafluoropropane (HCFC - 244bb) in a reactor such as a vapor - phase reactor according to the following reaction scheme.

Chem.

[0019] More specifically, the equilibrium equation of Process 3 can be the following equation.

Chem.

[0020] FIG. 1 is a process flow diagram showing Process 3 of a process for manufacturing 2,3,3,3 - tetrafluoropropene according to some embodiments of the present disclosure. FIG. 1 shows that the process flow 10 of Process 3 can include the flow of a composition 12 containing liquid 244bb flowing into a heater 14. The flow 12 of the composition containing liquid 244bb can be from any process according to the above - mentioned Process 2 or from any other source of liquid 244bb. The flow 12 of the composition can also include residues such as unreacted 1233xf, recycled 1234yf, HF, HCl, and trace impurities.

[0021] Heater 14 can heat liquid 244bb to at least its dew point at the process pressure, thereby creating a vaporized flow 16 of 244bb that can be saturated vapor or superheated steam. The process pressure may be lower than atmospheric pressure or may exceed atmospheric pressure. The process pressure can be a low gauge pressure of -4 pounds per square inch (psig) (-28 kilopascals (kPa)), 0 psig (0 kPa), 20 psig (138 kPa), 30 psig (207 kPa), or 40 psig (276 kPa), or a high gauge pressure of 80 psig (552 kPa), 110 psig (758 kPa), 150 psig (1,034 kPa), 200 psig (1,379 kPa), or 300 psig (2,068 kPa), or can be within any range defined between any two of the aforementioned values, such as, for example, -4 psig (-28 kPa) to 300 psig (2,068 kPa), 0 psig (0 kPa) to 200 psig (1,379 kPa), 20 psig (138 kPa) to 150 psig (1,034 kPa), 30 psig (207 kPa) to 110 psig (758 kPa), 40 psig (276 kPa) to 80 psig (552 kPa), 80 psig (552 kPa) to 150 psig (1,034 kPa), or 40 psig (276 kPa) to 110 psig (758 kPa).

[0022] Heater 14 can heat liquid 244bb to a low temperature of 40°F (4°C), 100°F (38°C), 150°F (66°C), 200°F (93°C), or 250°F (121°C), or a high temperature of 300°F (149°C), 350°F (177°C), 400°F (204°C), 450°F (232°C), or 500°F (260°C), vaporize it, and optionally superheat it further, or, for example, 40°F (40°C) to 500° It can be within any range defined between any two of the aforementioned values, such as F(260 °C), 100 °F (38 °C) to 450 °F (232 °C), 150 °F (66 °C) to 400 °F (204 °C), 200 °F (93 °C) to 350 °F (177 °C), 250 °F (121 °C) to 300 °F (149 °C), or 400 °F (204 °C) to 500 °F (260 °C).

[0023] The vaporization flow 16 of 244bb can pass through the heat exchanger 18 to increase the temperature of the vaporized 244bb and create a superheated vaporization flow 20 of 244bb. The heat exchanger 18 can be an economizer or exchanger for recovering heat from the reactor effluent, as described below. The heat exchanger 18 can be, for example, a shell and tube heat exchanger. The superheated vaporization flow 20 of 244bb can pass through the superheater 22 to further increase the temperature of the vaporized 244bb and create a further superheated flow 24 of 244bb. The superheater 22 can be an electric heater known in the art, although other types of heaters are contemplated. The temperature of the further superheated flow 24 of 244bb can be as low as about the same as 575°F (302°C), 610°F (321°C), 650°F (343°C), 690°F (366°C), 735°F (392°C), 780°F (416°C), 830°F (443°C), 850°F (454°C), 870°F (466°C), 900°F (482°C), 930°F (499°C), or 960°F (516°C), or as high as about the same as 1,040°F (560°C), 1,080°F (582°C), 1,120°F (604°C), 1,160°F (627°C), or 1,200°F (649°C), or can be within any range defined between any two of the aforementioned values, such as, for example, 575°F (302°C) to 1,200°F (649°C), 850°F (454°C) to 1,200°F (649°C), 870°F (466°C) to 1,160°F (627°C), 900°F (482°C) to 1,120°F (604°C), 930°F (499°C) to 1,080°F (582°C), 960°F (516°C) to 1,040°F (560°C), or 870°F (466°C) to 930°F (499°C).

[0024] The further heated flow 24 of 244bb can be supplied to reactor 26. As shown in FIG. 1, reactor 26 can include a plurality of reactor sections 28a, 28b, 28c, and 28d that are fluidly connected to each other by reactor flows 30a, 30b, and 30c. Each of reactor sections 28a, 28b, 28c, 28d can include at least one immersion heater that includes a heater surface configured to contact the heated 244bb. Within reactor 26, the heated 244bb is contacted with the heater surface over a contact time, during which at least a portion of the 244bb in the composition is dehydrochlorinated to produce 1234yf and HCl is produced as a byproduct (Equation 1). The contact time can be less than 10 seconds. The contact time can be as short as 0.1 second, 0.5 second, 1 second, 2 seconds, 3 seconds, or 4 seconds, or as long as 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, or 10 seconds, or can be within any range defined between any two of the foregoing values, for example, 0.1 second to 10 seconds, 0.5 second to 9 seconds, 1 second to 8 seconds, 2 seconds to 7 seconds, 3 seconds to 6 seconds, 4 seconds to 5 seconds, 0.1 second to 9 seconds, or 5 seconds to 9 seconds.

[0025] The heater surface can have a low surface temperature of 850°F (454°C), 870°F (466°C), 900°F (482°C), 940°F (504°C), 965°F (518°C), 990°F (532°C), 1,010°F (543°C), or 1,030°F (554°C), or a high surface temperature of 1,080°F (585°C), 1,110°F (593°C), 1,140°F (616°C), 1,170°F (632°C), or 1,200°F (649°C), or, for example, 850°F (454°C) to 1,200°F (649°C), 870°F (466°C) to 1,200°F (649°C), 940°F (504 It can be within any range defined between any two of the aforementioned values, such as between 300°F (149℃) and 1,200°F (649℃), between 965°F (512℃) and 1,170°F (632℃), between 990°F (532℃) and 1,140°F (616℃), between 1,010°F (543℃) and 1,110°F (593℃), between 1,030°F (554℃) and 1,080°F (585℃), or between 965°F (518℃) and 1,010°F (543℃).

[0026] In some embodiments, the heater surface can be the catalyst surface with respect to the reaction scheme shown above with reference to Step 3. In some embodiments, the catalyst surface can include electroless nickel, nickel, stainless steel, nickel-copper alloy, nickel-chromium-iron alloy, nickel-chromium alloy, nickel-chromium-molybdenum alloy, or combinations thereof.

[0027] In some other embodiments, the heater surface is not the catalyst surface with respect to the reaction scheme shown above with reference to Step 3. In some embodiments, the heater surface includes gold, platinum, or combinations thereof.

[0028] The deposition of carbon deposits (also called coking) on the heater surface of the reactor 26 can reduce the heat transfer between the heater surface and 244bb. The reactor 26 must be taken offline periodically so that the carbon deposits can be removed. The reduction of carbon deposits can reduce the frequency with which the reactor 26 must be shut down for cleaning and increase the operating time and productivity of the reactor 26. It is considered that carbon deposits can be generated according to the following reaction scheme.

Chemical formula

[0029] Accordingly, the degree of carbon formation can be indicated by measuring the concentration of 1,1,1,2 - tetrafluoroethane (HFC - 134a or 134a) downstream of reactor 26. Reduction of carbon formation can be indicated by a decrease in the concentration of 134a. Surprisingly, higher surface temperatures, such as from about 975°F to about 1005°F, when combined with short contact times, such as less than 10 seconds, were found to be able to dehydrochlorinate 244bb to produce 1234yf while producing less carbon deposit. This is unexpected as one of ordinary skill in the art would not expect less carbon deposit at higher temperatures.

[0030] A flow 32 containing 1234yf, HCl, and unreacted 244bb flows from reactor 26, passes through heat exchanger 18, and can supply additional heat to the vaporization flow 16 of 244bb as described above, and can cool the flow 32 of 1234yf, HCl, and unreacted 244bb. The cooled flow 34 of 1234yf, HCl, and unreacted 244bb can flow to a distillation column 36 where at least a portion of the unreacted 244bb can be separated from the 1234yf and HCl into a recycle flow 38 of unreacted 244bb. In some embodiments, substantially all of the unreacted 244bb can be separated from the 1234yf and HCl into the recycle flow 38. The recycle flow 38 of unreacted 244b b can merge with the flow 12 of the composition containing 244bb flowing into heater 14 as shown in FIG. 1.

[0031] The flow 40 of separated 1234yf and HCl can be processed to separate HCl from 1234yf by passing through an HCl separation unit 42 to remove HCl and produce a product stream 44 containing 1234yf. In the embodiment shown in FIG. 1, the HCl separation unit 42 is a distillation column that produces an anhydrous HCl stream 45 in addition to the product stream 44. In other embodiments, the HCl separation unit 42 can be a falling-film HCl absorber that uses a recycled dilute HCl solution and fresh make-up water. In still other embodiments, the HCl separation unit 42 can be an adiabatic HCl absorber, as is known in the art. In yet other embodiments, the HCl separation unit 42 can be a scrubber that uses an aqueous basic solution.

[0032] The product stream of 1234yf can be a crude product stream that includes, in addition to the above 134a, by-products such as 3,3,3-trifluoro-1-propyne (TFPY), and any 244bb not separated into the recycle flow 38. The by-products can be separated from the 1234yf in the product stream 44 by further processing (not shown) known in the art.

[0033] In some embodiments, the product stream 44 can contain 1234yf at a concentration greater than 99.10 weight percent (wt%), 99.20 wt%, 99.30 wt%, 99.40 wt%, 99.50 wt%, 99.60 wt%, 99.70 wt%, 99.80 wt%, 99.90 wt%, 99.91 wt%, 99.92 wt%, or 99.93 wt%, or any value between any two of the foregoing values.

[0034] In some embodiments, the product stream 44 can contain 134a at a concentration of less than 0.1 wt%, 0.05 wt%, 0.02 wt%, 0.010 wt%, 0.009 wt%, 0.008 wt%, 0.007 wt%, 0.006 wt%, 0.005 wt%, 0.004 wt%, 0.003 wt%, 0.002 wt%, or 0.001 wt%, or less than any value between any two of the foregoing values. The low value of 134a in the product stream 44 indicates low carbon deposition in the reactor 26. It has been found that the carbon deposition in the reactor 26 in the process flow 10 can be reduced by about 80% to 90% compared to prior art processes. Reducing carbon deposition can reduce the downtime and cost of the reactor associated with the need to periodically clean carbon from the reactor 26.

[0035] For the sake of consistency, the concentrations of the product stream 44 described herein do not include 244bb. That is, 244bb in the product stream 44 is not included with respect to determining the weight percent of 1234yf, 134a, or other component concentrations in the product stream 44.

[0036] FIG. 2 is a process flow diagram showing step 3 of another process for manufacturing 2,3,3,3 - tetrafluoropropene according to some embodiments of the present disclosure. FIG. 1 shows that the process flow 46 of step 3 can be the same as the process flow 10 shown in FIG. 1, except that the reactor 26 is replaced by a two - stage reactor 48 and the vaporization flow 16 of 244bb is split into a first portion 50 and a second portion 52. The first portion 50 can flow through the heat exchanger 18 as described above with respect to the vaporization flow 16 of 244bb with reference to FIG. 1 to create a superheated vaporization flow 20 of 244bb. The superheated vaporization flow 20 of 244bb can pass through the superheater 22 to further increase the temperature of the vaporized 244bb and create a further superheated flow 24 of 244bb that is supplied to the reactor 48. The second portion 52 is supplied to the reactor 48 without passing through the heat exchanger 18 and is present.

[0037] As shown in FIG. 2, the reactor 48 can include a first stage 54 and a second stage 56. The first stage 54 can include a plurality of reactor sections 58a, 58b, 58c, and 58d that are fluidly connected to each other by reactor flows 60a, 60b, and 60c. The second stage 56 can include a plurality of reactor sections 62a, 62b, 62c, and 62d that are fluidly connected to each other by reactor flows 64a, 64b, and 64c. Each of the reactor sections 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d can include at least one immersion heater that includes a heater surface configured to contact superheated 244bb. Similar to the case of the reactor 26 described above, within the reactor 48, the superheated 244bb is contacted with the heater surface over a contact time, and during this contact time, at least a portion of the 244bb in the composition is dehydrochlorinated to produce 1234yf and produce HCl as a by-product (Equation 1). The contact time and temperature of the process flow 46 can be as described above for the process flow 10.

[0038] The inter-stage flow 66 fluidly connects the first stage 54 to the second stage 56, and the second stage 56 is downstream of the first stage 56. The further superheated flow 24 of 244bb from the first portion 50 flows into the first stage 54. The second portion 52 can flow into the second stage 56 together with the inter-stage flow 66 from the first stage 54 and can cool the inter-stage flow 66 before entering the second stage 56. The cooler inter-stage flow 66 entering the second stage 56 can allow the immersion heaters in the reactor sections 62a, 62b, 62c, and 62d of the second stage to operate at a higher heater surface temperature. Without being bound by any theory, it is believed that by operating at a higher heater surface temperature, the conversion of 244bb to 1234yf can be optimized without causing a higher temperature in the flow including 1234yf, HCl, and unreacted 244bb 32 flowing from the reactor 48.

[0039] The first portion 50 flowing through the heat exchanger 18 is less than the vaporization flow 16 of 244bb flowing through the heat exchanger 18 as described in FIG. 1. Thus, the temperature of the superheated vaporization flow 20 of 244bb can be significantly higher than a given flow 32 containing 1234yf, HCl, and unreacted 244bb from the reactor 48. Since the superheater 22 may require less heating the higher the temperature of the superheated vaporization flow 20 of 244bb, its size can be reduced. A smaller superheater 22 can result in significant capital and operating cost savings.

[0040] In some embodiments according to the present disclosure, the immersion heater is an electric immersion heater. In some embodiments, the electric immersion heaters can be individually controlled to provide a desired heater surface temperature in different sections of the reactor. In some embodiments, the electric immersion heater can include a tubular body surrounding an electrical resistance wire that generates heat when current passes through the wire. Such an electric immersion heater can include a ceramic insulating material such as magnesium oxide between the wires within the same tube to conduct heat from the wire to the surrounding tubular body and at the same time electrically insulate the wires from each other. The outer surface of the tubular body can form the heater surface as described above. The ceramic insulating material is also a safety mechanism. The ceramic insulating material is mostly non-reactive with respect to the above-mentioned feed, product, or by-product. Even if a leak occurs in the tubular body, the ceramic insulating material can prevent the leak from spreading further beyond the electric immersion heater.

[0041] In some embodiments, the reactor sections 28a, 28b, 28c, 28d, 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d can be shell-and-tube reactors in which 244bb flows through the shell, and the tubes are replaced by electric heater elements. In some other embodiments, the reactor sections 28a, 28b, 28c, 28d, 58a, 58b, 58c, 58d, 62a, 62b, 62c, and 62d can be U-tube reactors having electric flange immersion heaters.

[0042] In the embodiments shown in FIGS. 1 and 2, a reactor or reactor stage having four sections is shown. However, it is understood that the present disclosure includes embodiments having less than four sections or more than four sections. It is also understood that embodiments may include two or more reactors in series and / or in parallel configurations to dehydrochlorinate 244bb to produce 1234yf.

[0043] In the above embodiment, the heat exchanger 18 is used to improve the energy efficiency of the process for producing 2,3,3,3-tetrafluoropropene. However, it is understood that some embodiments may not include the heat exchanger 18.

[0044] In the above embodiment, the superheater 22 further superheats the flow of 244bb to the reactor. However, it is understood that some embodiments may not include the superheater 22 and may provide further superheating of the flow of 244bb by the reactor.

[0045] As used herein, the phrase "within any range defined between any two of the foregoing values" means that any range can be selected from any two of the values listed prior to such phrase, regardless of whether those values are in the lower portion of the enumeration or the higher portion of the enumeration. For example, a pair of values may be selected from two lower values, two higher values, or a lower value and a higher value.

[0046] The invention has been described as an exemplary design, but the invention can be further modified within the spirit and scope of the present disclosure. Further, this application is intended to embrace such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.

Examples

[0047] Example 1 A composition containing 96.0 wt% of 244bb, 3.5 wt% of 1233xf, and 0.5 wt% of other materials (measured by gas chromatography) was vaporized at 70 psig to at least its dew point. The vaporized composition was superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated vaporized composition was introduced into a reactor containing four electrically heated sections. The superheater was configured such that the gas velocity was at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor was maintained between 993°F and 997°F at an average heater surface temperature of 995°F. The superheated vaporized composition passed through the reactor with an average contact time of 5.46 seconds based on the inlet conditions to the reactor. The output of the reactor was led to a distillation column to separate unreacted 244bb from 1234yf and HCl. The bottom stream of the distillation output containing unreacted 244bb was recovered for recycling. The overhead stream containing 1234yf and HCl was led to another distillation column to separate HCl as an overhead product and produce a crude product stream containing 1234yf. The process was maintained for 80 hours for an overall conversion of 21.3% of 204bb to 1234yf. The product stream was analyzed by gas chromatography using techniques well known in the art. The results are shown in the following table. Example 2

[0048] A composition containing 96.2 wt% of 244bb, 3.6 wt% of 1233xf, and 0.2 wt% of other materials (measured by gas chromatography) was at 70 psig at least It was also vaporized to its dew point. The vaporized composition was superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated vaporized composition was introduced into a reactor containing four electrically heated sections. The superheater was configured such that the gas velocity was at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor was maintained at 980°F - 995°F with an average heater surface temperature of 988°F. The superheated vaporized composition passed through the reactor with an average contact time of 5.46 seconds based on the inlet conditions to the reactor. The output of the reactor was led to a distillation column to separate the unreacted 244bb from 1234yf and HCl. The bottom stream of the distillation output containing the unreacted 244bb was recovered for recycling. The overhead stream containing 1234yf and HCl was led to another distillation column to separate HCl as an overhead product and produce a crude product stream containing 1234yf. The process was maintained for 92 hours for an overall conversion of 20.5% of 204bb to 1234yf. The product stream was analyzed by gas chromatography using techniques well known in the art. The results are shown in the following table. Example 3

[0049] A composition containing 97.6 wt% of 244bb, 2.0 wt% of 1233xf, and 0.4 wt% of other materials (measured by gas chromatography) was vaporized at 70 psig to at least its dew point. The vaporized composition was superheated in a heat exchanger and then further superheated to 900°F in a superheater. The further superheated vaporized composition was introduced into a reactor containing four electrically heated sections. The superheater was configured such that the gas velocity was at least twice the gas velocity in the reactor to minimize coking in the superheater. The heater surface temperature in the reactor was maintained between 989°F and 998°F at an average heater surface temperature of 993.5°F. The superheated vaporized composition passed through the reactor with an average contact time of 8.4 seconds based on the inlet conditions to the reactor. The output of the reactor was led to a distillation column to separate unreacted 244bb from 1234yf and HCl. The bottom stream of the distillation output containing unreacted 244bb was recovered for recycling. The overhead stream containing 1234yf and HCl was led to another distillation column to separate HCl as an overhead product and produce a crude product stream containing 1234yf. The process was maintained for 604 hours for an overall conversion of 30.3% of 204bb to 1234yf. The product stream was analyzed by gas chromatography using techniques well known in the art. The results are shown in the following table. Comparative Example

[0050] A composition containing 97.9 wt% of 244bb, 1.8 wt% of 1233xf, and 0.2 wt% of other materials (measured by gas chromatography) was vaporized at 70 psig to at least its dew point. The vaporized composition was heated in a heat exchanger and then superheated in a superheater to a temperature in the range of 740°F to 800°F. The superheated vaporized composition was introduced into a conventional shell and tube reactor, and the composition was contained in the reactor tubes. The reactor tubes were surrounded by a shell containing a heating medium. The mixed average temperature inside the reactor tubes was maintained at 900°F, and the surface temperature inside the reactor tubes (in contact with the composition) was maintained at about 909°F. The superheated vaporized composition passed through the reactor with an average contact time of 58 seconds based on the inlet conditions to the reactor. The output of the reactor was led to a distillation column to separate unreacted 244bb from 1234yf and HCl. The bottom stream of the distillation output containing unreacted 244bb was recovered for recycling. The overhead stream containing 1234yf and HCl was led to another distillation column to separate HCl as an overhead product and produce a crude product stream containing 1234yf. The process was maintained for 396 hours for an overall conversion of 29.2% of 204bb to 1234yf. The product stream was analyzed by gas chromatography using techniques well known in the art. The results are shown in the following table.

Table 1

[0051] As shown in the table, Examples 1 - 3 by processes with higher heater surface temperatures and shorter contact times produced significantly less 134a, which correlates with significantly less carbon deposition (coking) in the reactor.

Claims

1. A process for producing 2,3,3,3-tetrafluoropropene (HFO-1234yf), the process comprising: supplying a composition comprising 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb) to a reactor comprising a heater surface having a surface temperature above about 850°F (454°C); contacting the composition with the heater surface for a contact time of less than 10 seconds to dehydrochlorinate a portion of the HCFC-244bb to produce HFO-1234yf.

2. The dehydrochlorination of the portion of the HCFC-244bb produces hydrochloric acid (HCl), and the process further comprises: supplying the HFO-1234yf, HCl, and unreacted HCFC-244bb from the reactor to a distillation column; separating the HFO-1234yf and the HCl from at least a portion of the HCFC-244bb within the distillation column; recycling the separated HCFC-244bb to the reactor; supplying the HFO-1234yf and the HCl to an HCl separation unit; separating the HCl from the HFO-1234yf to form a product stream comprising the HFO-1234yf; and the product stream comprises the HFO-1234yf at a concentration of greater than 99.1 wt% without containing HCFC-244bb and 1,1,1,2-tetrafluoroethane at a concentration of less than 0.1 wt% without containing HCFC-244bb, and exhibits a low rate of carbon deposition within the reactor. The process according to claim 1.

3. A process for producing 2,3,3,3-tetrafluoropropene (HFO-1234yf), the process comprising: vaporizing a composition comprising 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb); dividing the composition into a first portion and a second portion; heating the first portion of the vaporized composition to a temperature of about 575°F (302°C) to 1,200°F (649°C); supplying the composition to a reactor comprising a heater surface having a surface temperature above about 850°F (454°C), the reactor comprising a first stage and a second stage downstream of the first stage, the first portion being supplied to the first stage and the second portion being supplied to the second stage. A process comprising contacting the composition with the surface of the heater for a contact time of less than 10 seconds to dehydrochlorinate a part of the HCFC-244bb to produce HFO-1234yf.

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